The sounds that the USB HDD makes vary from person to person. I can only explain my point of view. Yes, it is audible. If the HDD is placed on a hollow body such as a carcass, etc., the whole thing is amplified even more. Not for rooms where it has to be quiet.
But if the volume changes over time, I would still consider filing a warranty claim. The HDD should not be louder than it is now when it is idle or in use (R/W).
mine, too, makes a more or less regular "parasite/spasm" noise in addition to the "normal" operating noise. I hesitated to send it back under warranty, but afterwards I kept it like that (it's in the cellar... not a disturbing noise), and for the moment it's still working "normally" with these noises.
I've got lots of others in the same series, but up to 10-14 Tb, they don't make the same noise at all.